I've found that doing garden rejuvenation is a natural segue from pure maintenance to design, and clients are more likely to see you as a designer when they have seen rejuvenation/rehab work. Garden rejuvenation (and advertising it) some time ago, and that requires some design skill -- often, you have to replace tracts of a garden with something entirely new and different, or tweak a former design to fit current needs.

Maybe you could try that approach and see how it flys.

I do garden design and maintenance, but having started from scratch, I didn't have a maintenance base.

I have found that I get most of my clientele with advertising focused on specific targets.

I fix mistakes made by "landscapers" who really are lawn jockeys or hardscapers, but in trying to be full service, they stop at the wholesale nursery and buy some stuff to stick in. No concern whether it belongs where they put it, will thrive, or even looks good. As an example, I moved a row of 15 Elegans hostas, planted along the south face of a retaining wall in full sun. What were they thinking??

I also reclaim overgrown or out of control landscapes. Mostly this is new homeowners who bought a property where the former owner went to extremes. I've seen a lot of homes formerly owned by elderly gardeners who spent their retirement gardening. When the home is sold, new owners don't have the time or knowledge to devote to it. I also see a lot of homes where someone xeriscaped and the next owner hates it.

A lot of what I do is by word of mouth. I've started with one house in a neighborhood and ended up with four other homes, plus the mailman who delivered that route. ASK for referrals! I made nice with the mailman, and he got me two of the other homes.

I advertise on Craigslist. Knowing who seems to be my biggest audience, I write my ads to attract that type of attention. There are literally hundreds of landscaping ads on CL, however 99% of them are after lawns and hardscape. I get specific as to what I do and don't do, (I have absolutely no desire to build a patio!) and I try to write the ad in such a way so people will know that while I'm not cheap, since I work with their existing "bones" my renovation is less than a complete landscaping.

Since you have an affluent maintenance base, have you tried making redesign suggestions to them? I'm finding that people here are going for ideas that will lower maintenance or conserve water. I'm redesigning beds for one woman right now who has a $600 a month water bill! Ouch. She is willing to spend $1500 for a rain barrel system, not only to save money, but to be green.

Try advertising playing your strengths against the "hot" buttons for your area.

And all that said, now I have to get to work. Good luck!